Discharge lamp lighting device

Abstract

A discharge lamp lighting device includes a control unit adapted to control a frequency of the AC electric current supplied to a discharge lamp by a feeding unit, in different manners within a first term and a second term which are alternately repeated, the control unit is adapted to control the frequency of the AC electric current such that, within the first term, the frequency of the AC electric current becomes at least one frequency out of plural set frequencies, and is further adapted to control the frequency of the AC electric current, based on a predetermined frequency and an electric current within the previous first term, such that, within the second term, the frequency of the AC electric current becomes a frequency lower than this predetermined frequency.

1 . A discharge lamp lighting device comprising:
 a feeding unit adapted to supply an AC electric current to a discharge lamp having a pair of electrodes placed to oppose each other within a discharge container which encloses a predetermined gas; and   a control unit adapted to control a frequency of the AC electric current supplied to the discharge lamp by the feeding unit, in different manners within a first term and a second term which are alternately repeated;   wherein the control unit is adapted to control the frequency of the AC electric current such that, within the first term, the frequency of the AC electric current becomes at least one frequency out of plural set frequencies, and is further adapted to control the frequency of the AC electric current, based on a predetermined frequency and an electric current within the previous first term, such that, within the second term, the frequency of the AC electric current becomes a frequency lower than this predetermined frequency.   
     
     
         2 . The discharge lamp lighting device according to  claim 1 , wherein the control unit is adapted to control the frequency of the AC electric current such that the frequency of the AC electric current becomes a predetermined frequency out of plural set frequencies, within the first term. 
     
     
         3 . The discharge lamp lighting device according to  claim 1 , wherein the control unit is adapted to control the frequency of the AC electric current such that, within the first term, the frequency of the AC electric current becomes at least two frequencies out of the plural set frequencies, and is further adapted to control the frequency of the AC electric current, based on an electric current and a frequency having a largest time ratio within the previous first term, such that, within the second term, the frequency of the AC electric current becomes a frequency lower than this frequency. 
     
     
         4 . The discharge lamp lighting device according to  claim 1 , wherein the control unit is adapted to control the frequency of the AC electric current such that, within the first term, the frequency of the AC electric current becomes at least two frequencies out of the plural set frequencies, and is further adapted to control the frequency of the AC electric current, based on an electric current and a lowest frequency within the previous first term, such that, within the second term, the frequency of the AC electric current becomes a frequency lower than this frequency. 
     
     
         5 . The discharge lamp lighting device according to  claim 1 , wherein
 the plural frequencies to be set within the first term are set to be respective frequencies provided by multiplying a highest frequency out of the plural frequencies by the inverses of respective natural numbers, and   the frequency within the second term is set to be a frequency provided by multiplying the highest frequency by the inverse of a natural number.   
     
     
         6 . The discharge lamp lighting device according to  claim 1 , wherein the control unit is adapted to control the frequency of the AC electric current in such a way as to alternately repeat a basic term and a lower-frequency term, the basic term being provided for controlling the frequency of the AC electric current in different manners within the first term and the second term which are alternately repeated, and the lower-frequency term being provided for controlling the frequency of the AC electric current such that the frequency of the AC electric current becomes a frequency lower than a lowest frequency within the previous basic term. 
     
     
         7 . The discharge lamp lighting device according to  claim 6 , wherein the control unit is adapted to control the frequency of the AC electric current, based on an electric current and a predetermined frequency within the previous basic term, such that the frequency of the AC electric current becomes a frequency lower than the predetermined frequency, within the lower-frequency term. 
     
     
         8 . The discharge lamp lighting device according to  claim 6 , wherein
 the plural frequencies to be set within the first term are set to be frequencies provided by multiplying a highest frequency out of the plural frequencies by the inverses of respective natural numbers,   the frequency within the second term is set to be a frequency provided by multiplying the highest frequency by the inverse of a natural number, and   the frequency within the lower-frequency term is set to be a frequency provided by multiplying the highest frequency by the inverse of a natural number.